S2Q1 · Reverse Each Word

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⚡ Quick Reference

Function: reverse_each_word(words: list) -> list

Core idea: Apply [::-1] to every string in the list via a list comprehension.

def reverse_each_word(words):
    return [w[::-1] for w in words]

Key rules: - Reverse each string independently - Return a new list -- don't modify the original - Empty list input returns an empty list

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Problem Statement

Problem

Write a function reverse_each_word(words) that takes a list of strings and returns a new list where every string is reversed. All elements are guaranteed to be strings.

Examples:

Call

reverse_each_word(["apple", "cat", "python"])

Output

['elppa', 'tac', 'nohtyp']

Call

reverse_each_word(["hi", "go"])

Output

['ih', 'og']

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Understanding the problem

Each word is reversed independently -- the order of words in the list stays the same, only the characters within each word are reversed:

Input word	Reversed
"apple"	"elppa"
"cat"	"tac"
"python"	"nohtyp"

[::-1] works on any sequence

The slice s[::-1] reverses any sequence -- strings, lists, or tuples. For strings it returns a new string (strings are immutable in Python), so there's no in-place modification to worry about.

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Solution approaches

ExplanatoryPythonicUsing lambda

def reverse_each_word(words: list) -> list:
    result = []
    for w in words:
        result.append(w[::-1])   # reverse each word and collect
    return result

def reverse_each_word(words: list) -> list:
    return [w[::-1] for w in words]

reverse_each_word = lambda words: list(map(lambda w: w[::-1], words))

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Key takeaways

01

Slice reversal: s[::-1]

A slice with step -1 traverses the sequence backwards, producing a reversed copy. It works on strings, lists, and tuples. For strings it returns a new string since strings are immutable.

02

List comprehension for element-wise transforms

[f(x) for x in iterable] applies a function to every element and collects the results into a new list. This is the idiomatic replacement for a for loop with .append().

03

map() as a functional alternative

map(lambda w: w[::-1], words) applies the reversal lazily to each element. Wrapping in list() materialises it. Both map and list comprehensions produce the same result -- use whichever reads more clearly.